Often times a metal part that is cast will require finish machining of certain details on the casting. Some methods of metal casting such as investment casting and die casting are more accurate than other methods, but typically there are certain tolerances or geometry that can not be cast and must be machined. It is common for a casting foundry to apply a machining allowance to their cast parts to allow for finish machining to final size.
Commonly a foundry, original equipment manufacturer (OEM) or other end user will supply the castings to a machine shop that will perform the precision machining operations and ship the parts back to the OEM.
The machining operations on ferrous castings in particular produces a large amount of dust from the graphite in the material. While some machine shops specialize in the machining of castings others will not want to take on casting machining jobs because the resulting dust from the casting can penetrate certain components of the machine tools used to machine the castings, thus accelerating machine wear and perhaps degrading the accuracy of the machine tool. Machining of castings often requires very robust machine tools and clamping setups to allow for the heavy cuts necessary to get ‘under the skin’ of the casting. Thus, machine shops taking on machining of castings will usually have dedicated facilities screened off from their other operations.
Machining of castings often requires different clamping or locating techniques to minimise errors from variations in the castings themselves. Casting machining specialists understand this and create location strategies to ensure consistent results.